Conventionally, a relay is often used to control a large current and a high voltage. However, in an engine control unit (ECU) for automobile electric components, an IPD (Intelligent Power Device) has been increasingly used instead of the relay in these years. The IPD is provided with a circuit having a protection function around a power MOS transistor, and has a built-in self-diagnosis function. The IPD is able to transmit a self-diagnosis result to a control microprocessor.
For example, as disclosed in Patent Literature 1 (JP 2000-299631A), a power supply control apparatus is known which corrects a detection result of a current detecting circuit on the basis of a detection result of a temperature detecting circuit. The power supply control apparatus includes a semiconductor switch, a temperature detecting circuit, a current detecting circuit, and a control circuit. The semiconductor switch is switched in accordance with a control signal supplied to a control signal input terminal, and controls a power supply from a power supply to a load. The temperature detecting circuit detects a temperature of the semiconductor switch. The current detecting circuit detects a current flowing through the semiconductor switch on the basis of a voltage generated due to an on resistance of the semiconductor switch. The control circuit corrects a detection result by the current detecting circuit on the basis of the detection result of the temperature detecting circuit, and controls the supply of the control signal on the basis of the corrected detection current.
In addition, in Patent Literature 2 (JP 2001-257573A), a technique related to an electric load driving IC used as a driving circuit in en electric control apparatus is disclosed. When an abnormal state is detected by an abnormal state detecting circuit, a power disconnection signal for forcibly fixing a control signal to a logic level on a disconnection side is generated continuously, and the signal is outputted from a signal output terminal to outside of the electric load driving IC.
In Patent Literature 3 (JP 2003-297929A), a circuit device having a plurality of overheat detecting circuits is disclosed. In a driver IC of the circuit device, the plurality of overheat detecting circuits are arranged in adjacent to each other. Each of the overheat detecting circuits includes a temperature detecting section, a reference voltage generating circuit, a comparator, and a switch circuit. The reference voltage generating circuit generates a reference voltage by using the resistance division of the plurality of resistances. The comparator compares an output voltage of the temperature detecting section with the reference voltage. The switch circuit is connected to at least one of the plurality of resistances in parallel, and is turned on and off on the basis of the control signal. When the temperature is rapidly increased by a short-circuited load, the switch circuit is turned off on the basis of the control signal from an overcurrent detecting circuit. When the switch circuit is turned off, the reference voltage rises to lower an overheat detection temperature. In this manner, the circuit device changes the reference voltage generated through resistance division of the plurality of resistances on the basis of the control signal of the overcurrent detecting circuit to lower the overheat detection temperature, and thereby prevents malfunction due to the heat transfer from an detection target of the overheat detecting circuit.
In addition, Patent Literature 4 (JP-A-Heisei 11-34765) discloses a circuit protection device for vehicle that two types of threshold values are set for overheat detection. The circuit protection device includes an output, circuit, a control circuit, an instructing circuit, and a setting circuit. The output circuit supplies electric power to drive a load driving device provided in a vehicle. The control circuit controls an amount of the power to be supplied from the output circuit. The instructing circuit detects a temperature, and outputs a change signal to change the power supply amount controlled by the control circuit when the detection temperature exceeds a predetermined threshold value. The setting circuit replaces the threshold value with a new threshold value of a different value when the amount of power supply exceeds a predetermined value. In this manner, the circuit protection device for vehicle sets two types of threshold values of the overheat detection.
The above-mentioned circuit detects an abnormal overheated state caused by a rapidly-increasing overcurrent and, prevents device destruction caused by the current surge. Accordingly, the threshold value in an overcurrent state is set to a value between a normal threshold value in a detection temperature (for example, 175° C.) and a normal threshold value in a recovery temperature (for example, 150° C.). Therefore, in a case of being in the overcurrent state for a long time due to a short-circuit of a load, the circuit is maintained in a high temperature state of the normal recovery temperature (for example, 150° C.) or more or of a rated operation temperature range (for example, 150° C.) or more, and accordingly a long-term reliability cannot be assured for a resin and a bonding wire.
It is said that an Au—Al bonding deterioration is an important defect mode in a power device and this is because a cower device operates under severe surrounding environment and large power in a common specification and becomes a high temperature. In an automobile field, an assurance requirement of the junction temperature of up to 170° C. is general for a elastic package. In this case, the solution of the Au—Al bonding deterioration problem becomes a key to assure the reliability.